911racer

Hi,

I see in the catalog that the 78-80 rear rotors are about twice as much as 81- rotors.

I thought that these were all the same. What is the difference in the two.

Thanks

Ed

Steve Weiner-Rennsport Systems

Hi Ed:

All 930 REAR rotors are the same.

78-79 front 930 rotors are different as they are full floating, 2-piece units.

80-89 front 930 rotors are 1-piece items (the spacer is incorporated into the hat) that are far less expensive than the 78-79 parts are.

911racer

Thanks,

I have my 79 930 rotors off right now and I can see that they are 2 piece.

Begs another question. What is the advantage of the 2 pc floating vs 1 pc.

I am looking at this for my race car and want the best setup. Is there a braking advantage, or is there a weight advantage one way or the other.

Why did the factory even start with the 2 pc setup.

Thanks

Ed

Steve Weiner-Rennsport Systems

Ed,...You've asked a big question here,...

Full floating rotors are two-piece rotor hat assemblies that are not directly bolted together.

Full floating rotors remain more concentric when very hot and are less likely to warp under high heat stresses. They are noisy for street use as you hear them "clunk" somewhat when they are cold. This is the sound of the drive dogs against the inner ring of the rotor. Porsche discontinued their use to aleviate those complaints and reduce costs.

Porsche started using floating rotors in their 908, 917 and on, race cars to minimize warpage and vibration. There is no weight advantage either way.

Personally, I would not use those rather fragile OEM Zimmerman rotors as they simply do not hold up well under track use and aggressive race pads. We use a custom Brembo 305x32mm 2-piece rotor/hat combo that is FAR tougher than the OEM Zimmermans.
IMHO, one of these days Porsche will discontinue these 2 year only rotor assemblies and force everyone with these to convert to the later 80-89 Zimmerman ones. That will require new 930 hubs as well.

911racer

Steve,

Thanks. This helps alot. I did not know that the zimmermans were originally OEM rotors. Thought that they were german aftermarket.

So the rotors that are on my 79 are just as suspect as new zimmermans ?

What is diferent about the 930 hubs between floating and non floating.

So, the answer also is, if I want to use 930 rotors on my racer, either get the aftermarket, or the one pc.

My application is fairly light. My racer is light, and my motor is weak, so not enough speed to need to haul it down too much. I am however really putting together a welth of knowlege on Porsche brakes.

What part of the stock brakes fail. I thought that the aftermarket hubs are alluminum. Is there a weight advantage with the aftermarket. Also, what is the cost.

Thanks

Ed

Steve Weiner-Rennsport Systems

Zimmerman rotors were OEM on all 930's until the C2 version came along. Zimmerman makes replacement rotors for all 911/930/964/993 cars and although cheaper than Brembo, they are NOT of the same quality & longevity.

In 1980, Porsche saved money by incorporating the wheel spacer into the hubs so if you want to use the much cheaper '80-on OEM rotors, you'll need the later hubs.

If you retain the 930 brakes, you'll need either OEM Zimmerman full floaters, the custom Brembo ones, or update to the '80-on setup only if your car has Turbo front flares.

LOL,..The stock brakes do not fail; in some cases they simply do not have enough stopping power for racing applications and the result is boiled fluid.

Many aftermarket brakes are of 2-piece design; a rotor and a machined, billet, hard anodized hat. This is to save weight when using very large and thick rotors. For example, the Brembo EVO 355mm brakes weigh far less than the Big Red TT 322mm brakes do and thats a biggie,.....

If you want prices, contact me directly.